shenandoahAdaptiveHeuristics.hpp

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#ifndef SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHADAPTIVEHEURISTICS_HPP
#define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHADAPTIVEHEURISTICS_HPP

#include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
#include "gc/shenandoah/shenandoahPhaseTimings.hpp"
#include "utilities/numberSeq.hpp"

class ShenandoahAllocationRate : public CHeapObj<mtGC> {
 public:
  explicit ShenandoahAllocationRate();
  void allocation_counter_reset();

  double sample(size_t allocated);

  double instantaneous_rate(size_t allocated) const;
  double upper_bound(double sds) const;
  bool is_spiking(double rate, double threshold) const;

 private:

  double instantaneous_rate(double time, size_t allocated) const;

  double _last_sample_time;
  size_t _last_sample_value;
  double _interval_sec;
  TruncatedSeq _rate;
  TruncatedSeq _rate_avg;
};

class ShenandoahAdaptiveHeuristics : public ShenandoahHeuristics {
public:
  ShenandoahAdaptiveHeuristics();

  virtual ~ShenandoahAdaptiveHeuristics();

  virtual void choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
                                                     RegionData* data, size_t size,
                                                     size_t actual_free);

  void record_cycle_start();
  void record_success_concurrent();
  void record_success_degenerated();
  void record_success_full();

  virtual bool should_start_gc();

  virtual const char* name()     { return "Adaptive"; }
  virtual bool is_diagnostic()   { return false; }
  virtual bool is_experimental() { return false; }

 private:
  // These are used to adjust the margin of error and the spike threshold
  // in response to GC cycle outcomes. These values are shared, but the
  // margin of error and spike threshold trend in opposite directions.
  const static double FULL_PENALTY_SD;
  const static double DEGENERATE_PENALTY_SD;

  const static double MINIMUM_CONFIDENCE;
  const static double MAXIMUM_CONFIDENCE;

  const static double LOWEST_EXPECTED_AVAILABLE_AT_END;
  const static double HIGHEST_EXPECTED_AVAILABLE_AT_END;

  friend class ShenandoahAllocationRate;

  // Used to record the last trigger that signaled to start a GC.
  // This itself is used to decide whether or not to adjust the margin of
  // error for the average cycle time and allocation rate or the allocation
  // spike detection threshold.
  enum Trigger {
    SPIKE, RATE, OTHER
  };

  void adjust_last_trigger_parameters(double amount);
  void adjust_margin_of_error(double amount);
  void adjust_spike_threshold(double amount);

  ShenandoahAllocationRate _allocation_rate;

  // The margin of error expressed in standard deviations to add to our
  // average cycle time and allocation rate. As this value increases we
  // tend to over estimate the rate at which mutators will deplete the
  // heap. In other words, erring on the side of caution will trigger more
  // concurrent GCs.
  double _margin_of_error_sd;

  // The allocation spike threshold is expressed in standard deviations.
  // If the standard deviation of the most recent sample of the allocation
  // rate exceeds this threshold, a GC cycle is started. As this value
  // decreases the sensitivity to allocation spikes increases. In other
  // words, lowering the spike threshold will tend to increase the number
  // of concurrent GCs.
  double _spike_threshold_sd;

  // Remember which trigger is responsible for the last GC cycle. When the
  // outcome of the cycle is evaluated we will adjust the parameters for the
  // corresponding triggers. Note that successful outcomes will raise
  // the spike threshold and lower the margin of error.
  Trigger _last_trigger;

  // Keep track of the available memory at the end of a GC cycle. This
  // establishes what is 'normal' for the application and is used as a
  // source of feedback to adjust trigger parameters.
  TruncatedSeq _available;
};

#endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHADAPTIVEHEURISTICS_HPP